JP2022510581A - Switch mode power converter - Google Patents

Abstract

The switch mode power converter has an inverter, a transformer having a primary winding and a secondary winding, and a first inductor in series with the primary winding. A second inductor that is magnetically coupled to the first inductor is provided, and the voltage at one end of the second inductor indirectly measures the voltage on the secondary side in the measurement on the primary side (that is,). , Used as a feedback signal to obtain an approximate value of the voltage on the secondary side).

Description

The present invention relates to switch mode power converters for use in, for example, LED drivers.

Switch mode power converters are well known for their use in both AC / DC conversion and DC / DC conversion. The resonant converter has, for example, a resonant circuit that can be a series or parallel resonant circuit. Resonant converters with an LLC resonant circuit with two inductances and one capacitance, or an LCC resonant circuit with two capacitances and one inductance, are well known for use within LED drivers. ..

The switch mode power converter can be configured or operated as a constant current or constant voltage source. A constant current source can be used to drive the LED configuration directly, thus allowing a single stage driver. Constant voltage sources can be used, for example, for LED modules that further have driver electronics to ensure the corresponding power supply to the LEDs. In that case, a predetermined current is drawn from the output voltage supplied by the constant voltage source.

Galvanic insulation is typically provided between the input and any output. A transformer is used to provide this insulation between the input power supply (typically the high voltage mains) and the load. The insulation requirement between the primary and secondary sides is usually that the primary and secondary windings of the transformer need to be physically separated, or that the primary and secondary windings are secondary. This means that the magnetic coupling with the next winding needs to be arranged so that it is not perfect. This imperfections in the magnetic coupling manifest themselves as the leakage inductance of the output transformer.

Current adjustments are typically used in LED driver applications, where the current adjustments control the switch mode power converter to supply the desired LED current on the secondary side. The tuning function can also be used, for example, to limit or control the output voltage produced by the LED driver in situations where the LED load is (or is) disconnected from the driver.

In that case, it is highly preferred that the circuit for measuring, limiting or controlling the output voltage of the driver be located on the primary side of the driver rather than on the isolated secondary side of the driver. In the latter case, the signal needs to be returned from the isolated secondary side to the primary side via a properly isolated path, such as through an optisolator.

Therefore, the current and / or voltage adjustment on the primary side is more cost effective and robust than the adjustment on the secondary side. First, high voltage or common mode insulation of the control circuit is not required in the primary control approach. Secondly, the auxiliary circuit that supplies power to the control unit is simplified. Moreover, the conditioning circuit located on the primary side can process any information from the mains in a very simple and effective way.

The voltage on the primary side of the output transformer is related to the output voltage of the driver, but the signal on the primary side is distorted due to the voltage drop through the leakage inductance of the output transformer.

In some cases, a separate winding for output voltage detection has a magnetic coupling with the secondary winding, which is actually a normal primary winding and a secondary winding. It is placed in the output transformer so that it has a much better magnetic coupling than the interval. In that case, the separate winding is electrically connected to the primary circuit. This is feasible unless a large amount of power needs to be transmitted through this sensing winding, so no large current needs to flow through the sensing winding and therefore the leakage inductance of the sensing winding. There is no large voltage drop through.

However, such detection windings with sufficient magnetic coupling with the secondary winding while maintaining the creepage and spatial distance associated with the insulation requirements between the primary and secondary sides of the output transformer. It is difficult to place.

Therefore, there is a need for an improved primary detection technique that produces a signal representing the output voltage of the driver and, among other things, compensates for the effects of the leakage inductance of the output transformer.

The present invention is defined by the claims.

According to an example according to certain aspects of the invention.
An inverter having a high-side switch and a low-side switch, wherein the high-side switch and the low-side switch are connected in series with a first node between the high-side switch and the low-side switch.
A transformer with a primary winding and a secondary winding,
A first inductor in series with the primary winding and connected to the primary winding at the second node,
A second inductor that is magnetically coupled to the first inductor, a second inductor that defines an output terminal at one end, and a controller for controlling the inverter, the voltage at the output terminal. A switch mode power converter with a controller having an input for receiving a signal obtained from is provided.

This power converter utilizes an additional (second) inductor coupled to the first inductor. The first inductor may be, for example, an already required part of a switch mode power converter such as used for energy storage or the formation of a portion of a resonant tank, or the first inductor. May be added for the purpose of making it possible to provide the output terminal. The first inductor is in series with the primary winding of the transformer. For example, the primary circuit already includes the first inductor that carries essentially the same current as the current flowing through the primary winding of the transducer. This may be the case, for example, in LCC converters and LLC converters.

The second inductor provides a simple way to measure the secondary side voltage on the primary side. The second inductor may be implemented by providing additional windings to the existing first inductor, in which case the two inductors have taps as defined by a single array. .. The voltage across the additional winding has the same shape and phase as the voltage across the leakage inductance, and the voltage signal error in the primary winding of the output transformer as caused by the leakage inductance. Used to compensate for. Therefore, the voltage detection of the secondary side voltage becomes more accurate based on the voltage detection on the primary side.

The detected voltage may then be used as part of the transducer control scheme. The detected voltage may be used, for example, to trigger protection when an overvoltage is detected at the output.

The transducer may further include a series capacitor in series with the first inductor and a capacitor in parallel with the secondary winding. This defines the LCC structure. Multiple secondary windings are possible.

The second inductor may have an inductance substantially equal to the combined primary side series leakage inductance of the transformer.

"Synthetic primary side series leakage inductance" in this context means the sum of the primary side leakage inductance and the reflected secondary side leakage inductance. In particular, this composition represents the effect of imperfect coupling between the primary and secondary sides of the transformer (in a model of the electrical properties of the transformer). In the case of multiple secondary windings, there can be multiple secondary leakage inductances, which can still be converted as secondary leakage inductances reflected to the primary side.

In this way, the inductance of the second inductor is equal to the leakage inductance it seeks to compensate. The leakage inductance may change with temperature, for example, and may not be known with high accuracy. Therefore, the second inductor is selected to have a value close to the leakage inductance.

Instead, the second inductor may have a turns ratio to the first inductor such that the second inductor has an inductance greater than the combined primary side series leakage inductance of the transformer.

In this way, the inductance of the second inductor is greater than the leakage inductance it seeks to compensate. In that case, the measured voltage can be scaled down.

The controller may have an input that is directly connected to the output terminal.

In that case, the voltage at the end of the second inductor functions as it is as a feedback signal of the controller.

In another example, the controller may have a coupling circuit for coupling a signal at the second node and a signal at the output terminal in order to obtain a detection signal supplied to the controller. ..

In this case, the voltage at each end of the second inductor is processed, eg, scaled, before being used as a feedback signal for the controller. This may be required, for example, because only the ratio of the integer number of turns of the second inductor to the integer number of turns of the first inductor is possible. In that case, a coupling function is used to improve the accuracy with which the leakage inductance is simulated.

The coupling circuit may have a resistor network for coupling the voltage at the second node and the voltage at the output terminal to supply the detection signal voltage.

This resistance network may be used to provide a weighted combination of voltages, or to derive any other function between the voltages at each end of the second inductor. May be done.

The coupling circuit may instead have a circuit for generating a detection signal current. Therefore, the feedback signal supplied to the controller can be voltage or current. However, even when a current is used as the feedback signal, it still depends on the voltage at the output node and thus on the voltage across the second inductor.

The second inductor may have a first end connected to the second node and may have the output terminal at the second end. In this manner, the second inductor is connected so that compensation for the combined leakage inductance (represented on the primary side) (eg, signal subtraction) is achieved by component placement.

In another example, the second inductor may have a grounded first end and may have the output terminal at the second end. In that case, the compensation (eg, signal subtraction) may be performed by the controller.

The transducer may have a resonant converter with a resonant tank connected to the first node, the resonant tank having the first inductor.

The transducer may further include a rectifier connected to the secondary winding and a storage capacitor over the output of the rectifier.

Therefore, the transducer supplies a DC output for a DC load.

In one set of examples, the rectifier has a four-diode bridge connected over the secondary winding. In another series of examples, the transformer is a series primary secondary winding and secondary secondary winding, the primary secondary winding and the secondary secondary winding. It has a primary secondary winding and a secondary secondary winding with a node defined between the wires, and the rectifiers (D1 to D4) have a two diode arrangement.

"Two-diode array" means that the function of the rectifier is carried out in only two unidirectional conduction paths. Each path may have a single diode, but of course the same function would be achieved if each path had multiple diodes in series.

The series connection of the first secondary winding and the secondary secondary winding may include a component between them, for example, the diode of the rectifier.

Therefore, it is possible to design different rectifiers depending on the design of the secondary side of the transformer.

The present invention
A converter as defined above, and a lighting circuit having a lighting load in parallel with the storage capacitor are also provided.

These and other embodiments of the invention will be described and clarified with reference to the embodiments below.

For a better understanding of the invention, and to show more clearly how the invention can be practiced, reference herein is made by way of illustration only.
An example of an LCC resonant switch mode power supply in an LED driver is shown. The power supply of FIG. 1 is shown with the leakage inductance shown. The power supply of FIG. 2 is shown in a state where the leakage inductance is converted to the primary side. The first example of the power source by this invention is shown. A second example of the power source according to this invention is shown. Different examples of input capacitors, output capacitors, transformer windings, and rectifier configurations that can be adopted are shown. Different examples of input capacitors, output capacitors, transformer windings, and rectifier configurations that can be adopted are shown. Different examples of input capacitors, output capacitors, transformer windings, and rectifier configurations that can be adopted are shown. Different examples of input capacitors, output capacitors, transformer windings, and rectifier configurations that can be adopted are shown. Two examples of coupling circuits that can be used to make a more accurate approximation to the leakage inductance are shown. Two examples of coupling circuits that can be used to make a more accurate approximation to the leakage inductance are shown.

The present invention will be described with reference to the drawings.

The detailed description and specific examples show exemplary embodiments of the device, system and method, but are for illustration purposes only and are not intended to limit the scope of the invention. Please understand. These and other features, embodiments and advantages of the devices, systems and methods of the invention will be better understood from the following description, the appended claims and the accompanying drawings. It should be understood that the figures are only schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figure to indicate the same or similar parts.

The present invention provides an inverter, a transformer having a primary winding and a secondary winding, and a switch mode power converter having a first inductor in series with the primary winding. A second inductor that is magnetically coupled to the first inductor is provided, and the voltage at one end of the second inductor indirectly measures the voltage on the secondary side in the measurement on the primary side (ie, the second). It is used as a feedback signal to obtain an approximate value of the voltage on the next side).

Although the present invention has been described with respect to an LCC resonant switch mode power supply, the invention is broader and applicable to other resonant tank designs and more broadly to switch mode power supplies.

FIG. 1 shows an example of an LCC resonant switch mode power supply in an LED driver with an isolated output.

The rectified main power input (or DC input of the DC / DC power converter) is supplied to the high-side MOSFET Mhs and the half-bridge inverter formed by the low-side MOSFET Mls. The inverter controls the conversion operation and uses feedback control or feedforward control to control the switching in order to produce the required output. Each switch of the inverter has its operating timing controlled by its gate voltage.

Resonance tank by the series capacitor Cs and series inductor Lres on the primary side of the output transformer 10 (having the primary side winding Lprim and the secondary side winding Lsec), and the parallel capacitor Cp on the secondary side of the output transformer 10. Is formed. There may be a plurality of parallel capacitors, for example, when there are a plurality of secondary windings. Note that Lprim and Lsec represent physical windings (where the components of the circuit can be connected).

The combined leakage inductance effectively increases the series inductor.
By placing the parallel capacitor Cp on the output side, the system still behaves as a tertiary system (with the inductor of the LCC tank, which is the sum of the leakage inductance and Lres, which will be further described later).

The output is supplied to the LED loads Led1 and Led2 via the diode bridge rectifiers D1 to D4 and the smoothing output capacitor Cout.

During the operation of the transducer, the controller (first shown in FIG. 4) is "essentially" complementary at a particular frequency in that there can be non-overlapping periods. ) Control the inverter switch in a way. A high gate drive signal turns one switch on and the other switch off, and a low gate drive signal turns one switch off and the other switch on.

In one known technique, the primary side circuit detects a variable indicating the time-averaged value of the current flowing through the circuit, eg, via a first or second switch. Information about the load is derived based on the measured current in the primary circuit. The measured current may have a direct relationship with the load.

FIG. 1 shows a full bridge rectifier on the secondary side and a single secondary winding Lsec, the single secondary winding Lsec coupled to the rectifier circuit at its end. Further below is an example of a circuit with multiple secondary windings. Such circuits may instead use a rectifier with only two diodes.

This is an example of an LCC resonant tank circuit, but LLC circuits and other resonant circuits, as well as non-resonant converters, are also possible.

The general operation of switch mode power converters, including resonant converters, will be well known to those of skill in the art.

The input to the resonant tank is node N1, where there is generally a square wave high voltage AC signal. It is a "generally" square wave signal in that gradient transitions can exist. If there is a tilt transition, both transistors must be off during such a tilt transition. The frequency of this AC signal coincides with the switching frequency of the transistors Mhs and Mls and is generally in the range of kHz, for example 10 kHz to 300 kHz. The amplitude of the signal at this location may change over time, for example, especially if the input is a rectified mains signal. In that case, there is a low frequency envelope of the high frequency signal at node N1.

The circuit of FIG. 1 includes a magnetic element Lres on the primary side that carries essentially the same current as the current flowing through the primary winding Lprim of the transformer 10.

The present invention preferably comprises providing an additional second inductor by providing an additional winding in the existing series inductor, in this example Lres. Therefore, in that case, there are a first inductor and a second inductor in series. The second inductor serves as a detection element.

The present invention is of particular interest for switch mode power conversion circuits with such series inductors. However, the series inductor (forming the first inductor) is in a circuit that does not yet have such a component, again with additional windings defining an additional second inductor, as before. May be added.

As a result, the voltage across the second inductor will have the same shape and phase as the voltage that drops over the leakage inductance of the transformer. When adding a dedicated magnetic element that functions as the first inductor, an inductance that has the least effect on the circuit function can be selected.

By subtracting the voltage across the second inductor from the voltage that can be measured on the primary side of the output transformer, a better and more accurate representation of the output voltage of the driver on the primary side is obtained. This subtraction may be performed by the controller or the circuit unit itself may perform the subtraction.

FIG. 1 shows a first node N1 between transistors and a second node N2 which is a second node N2 in which the primary winding is connected to the first inductor Lres in the second node N2. This node N2 is accessible and means that the voltage at this location can be monitored.

When the opposite side of the primary winding is grounded, the voltage to ground at node N2 is the voltage across the primary winding. Other series components, such as capacitors, are present, for example, between the other end of the primary winding Lprim and ground (or between the primary winding and the bus voltage supplied to the transistor inverter). May be good. The method of the invention can be applied to all of these possibilities.

As shown in FIG. 2, the non-ideal magnetic coupling between the primary and secondary sides of the transformer 10 can be described as the leakage inductance LsPrim on the primary side and the leakage inductance LsSec on the secondary side. .. In that case, the physical winding is represented by the combination of the leakage inductances LsPrim, LsSec and the ideal winding Lprim ", Lsec".

The voltage between node N2 and ground no longer represents a good secondary AC voltage between node N3 and node N4. A conceptual node N2 "is defined between the leakage inductance LsPrim on the primary side and the (ideal) primary winding Lprim", but this is not an accessible location in the circuit.

Leakage Inductances Voltages will be generated across LsPrim and LsSec by the currents flowing through these leakage inductances.

In FIG. 3, the leakage inductance LsSec on the secondary side is further converted to the primary side by scaling the impedance by the square of the transformation ratio. By combining the converted secondary side leakage inductance LsSec and the primary side leakage inductance LsPrim, a single total leakage inductance Ls is generated. Therefore, the leakage inductance on the secondary side is removed from the secondary side. Because it is instead represented on the primary side.

This combined primary side leakage inductance Ls can be regarded as the effective primary side and secondary side leakage inductance of the transformer, which is completely represented on the primary side of the transformer.

Here, a conceptual node N2'is defined between the combined primary side leakage inductance Ls and the primary side winding (representing) Lprim'. The voltage between this node N2'and ground is a better representation of the voltage across the primary winding Lprim', again as before, where it is accessible in the circuit. do not have.

Note that this is based on a model of the transformer, such as an ideal transformer that combines additional leak components (ie, parasitic components). Some such models are known as cantilever models, but other models may be used. Any suitable model can be used to represent all the leakage inductances on the primary side. It should be noted that the cantilever model provides a turn ratio for an ideal transformer, but said turn ratio can differ from the actual physical turn ratio. It should also be noted that as a result of the different representations of the transformer, the Lprim ", Lsec" and N2 "in FIG. 2 are different from the Lprim', Lsec' and N2' in FIG.

FIG. 4 shows a first example of a circuit according to the invention, based on the representation of the transformer of FIG. The first inductor is named LresA. A second inductor LresB having a first end connected to the second node N2, an output terminal at the second end, and a node N5 is provided. The first inductor and the second inductor are magnetically coupled, so here the first inductor is named LresA and the second inductor is named LresB. They may be combined into a single inductor with taps that define the junction between them. Separate inductors that share a magnetic core are also possible.

In FIG. 3, the current flowing through the first inductor Lres and the current flowing through the leakage inductance Ls are the same because they are in series, and therefore the shapes and phases of the voltages across the Lres and Ls are the same. Is.

As shown in FIG. 4, when adding a second inductor that results in a main first inductor LresA (formed from the main first winding) and a second inductor LresB (formed from additional windings). The magnetic coupling between LresA and LresB is considered to be good, which is very feasible as no significant insulation between the two windings is required. However, since a large current does not flow through the second inductor LresB, some leakage inductance will not be a problem.

The end of the second inductor on the opposite side of node N2 forms node N5, which is an output terminal. It connects to the controller 40. The controller 40 has an input 42 for receiving a voltage (or, in another example, a current) obtained from the voltage at the output terminal N5. In the example of FIG. 4, the controller input draws a minimum current so that the current does not substantially flow through the second inductor LresB.

By subtracting the voltage across the second inductor from the voltage that can be measured on the primary side of the output transformer (measured at node N2), the output voltage of the driver is better and more accurately represented on the primary side. You get things.

Since the voltage across the second inductor LresB has the same shape and phase as the voltage across the first inductor LresA, it also has the same shape and phase as the voltage across the leakage inductor Ls.

With an appropriate turns ratio between the inductor LresB and the inductor LresA, the voltage at node N5 can be adjusted to be essentially the same as the voltage at node N2', thus with node N3 and node N4. Provides a physically accessible node that carries a desirable and correct representation of the AC output voltage between. Therefore, the primary side measurement for limiting or controlling the output voltage of the driver becomes possible.

The turns ratio between LresB and LresA can only be adjusted to compensate for the nominal value of the primary leakage inductance Ls, so the voltage at node N5 (based on ground) is the leakage inductance. It is only essentially the same as the voltage at node N2'in FIG. 3 (relative to ground) for the nominal value of Ls.

Any deviation of the leakage inductance from the nominal value will result in imperfections in the voltage at node N5 as compared to the voltage at node N2'in FIG. However, the use of the signal at node N5 is still substantially better than the use of the signal at node N2.

In FIG. 4, one end of the second inductor LresB is connected to the node N2. This automatically generates a total at the node N5 by adding the voltage across the second inductor LresB to the voltage at the node N2. Therefore, the circuit provides the required addition / subtraction. However, this is not mandatory.

FIG. 5 shows a modified example in which one end of the second inductor LresB is grounded and the other end forms the node N5. In this manner, the insulating auxiliary windings can be used to compensate the primary voltage signal for the effects of the output transformer leakage inductance Ls. Addition / subtraction may be performed by another circuit or by a controller.

The fact that the second inductor LresB is magnetically coupled to the first inductor LresA is sufficient to make it possible to represent the leakage inductance Ls. This provides another method of generating a weighted sum of the voltage at the node N2 and the voltage across the second inductor LresB.

The above example uses a single secondary winding for the transformer, but there are other possibilities.

6-9 show other configurations to which the present invention can be applied, without showing the second inductor of the present invention. The second inductor can be added in the manner shown in FIG. 4 or 5.

FIG. 6 shows the secondary side of the transformer as two series secondary windings LsecA and LsecB. The junction between them supplies the first output terminal, and the terminals at the two ends are connected to the second output terminal via a two diode rectifier.

As shown, there may be a single parallel secondary capacitor Cp, or one capacitor per winding, i.e. a capacitor CpA parallel to LsecA and a capacitor CpB parallel to LsecB. May be good.

FIG. 7 shows a modification of FIG. 6, which has advantages in terms of insulation requirements between LsecA and LsecB and in terms of EMI performance. In this design, there is a parallel capacitor across each secondary winding and one of the diodes in the two diode rectifier is between the secondary windings.

In this case as well, the transformers in FIG. 7 are the first secondary winding LsecA and the secondary secondary winding LsecB in series, and the primary secondary winding LsecA and the first 1st secondary winding LsecA and 2nd secondary winding LsecB having a node (diode D2, one anode of the diode of the 2 diode rectifier) specified between the 2nd secondary winding LsecB. Has. The node defines a first output node. Diode D1, the cathode of another diode in the two diode rectifier is connected to the second output node.

In this case, it is not possible to place a single parallel capacitor Cp across the two secondary windings.

FIG. 8 shows another example of operating as a voltage doubler. Here, the output capacitor Cout is divided into two capacitors CoutA and CoutB arranged in series. There may be an additional capacitor Cout across the LED.

The transformer in FIG. 8 has a single secondary winding Lsec. The rectifier again has two diodes, again defining both output nodes in the same way as shown in FIG.

FIG. 9 shows a configuration in which series capacitors Cs at different positions are provided on the primary side. Capacitors Cs are formed as two series capacitors CsB and CsA between the bus voltage and ground. One end of the primary winding Lprim is connected to the junction between the two capacitors and the other end is connected to the first inductor Lres. The series capacitors may actually be located at CsA, CsB, or both (as shown), all in substance. Is equivalent to. This equivalence is because the bus voltage (which is the supply to the inverter) is usually disconnected from ground via a large capacitance.

Normally, Cs is large, so here the underside of the primary winding Lprim refers to the (almost) DC voltage at the node between CsA and CsB. Therefore, only the AC component of the voltage at the node N2 indicates the output voltage. When combining the voltage at the node N2 and the voltage across LresB according to the present invention, only the AC component needs to be considered.

If the first inductor (LresA in FIGS. 4 and 5) is the main component of the switch mode power converter (ie, the first inductor is simply added to allow the LresB inductor to be provided. If not), the power converter task of the inductor LresA leads the design of the inductor LresA (core, voids, turns, wires, etc.). In that case, the inductance of the main first inductor LresA is generally larger than the leakage inductance, and therefore also larger than the second inductor LresB. Therefore, the number of windings of the second inductor LresB is relatively small. Since the number of turns of the winding is an integer, it may not be possible to adjust the inductance of the second inductor LresB so that it exactly matches the nominal leakage inductance Ls.

One option is to use the next highest integer number of turns, or in fact, a higher number of turns for the second inductor LresB. This allows the voltage at the node N5 to be overcompensated for the influence of the leakage inductance Ls. This overcompensation may be taken into account based on the recognition that the node N2 is not compensated for the effect of the leakage inductance Ls.

In particular, a coupling circuit may be used to couple the signal at the second node N2 with the signal at the output terminal (node N5) to obtain the detection signal supplied to the controller. In this way, the amount of compensation can be adjusted to more closely match the effect of the leakage inductance Ls. For example, a weighted sum of the voltage at node N2 and the voltage at node N5, or other combinatorial function, may be used to represent the output voltage of the driver. In that case, this representation is used as a feedback signal to limit or control the output voltage.

FIG. 10A shows an example of a coupling circuit 10 in the form of a resistance network for coupling a voltage N2 at a second node N2 to a voltage at a node N5 to supply a detection signal voltage Vsense.

This circuit has a first resistance dividing circuit formed by resistors Ra and Rc, and a second resistance dividing circuit formed by resistors R1 and R2. This circuit is
Vsense = (V _N2 * Rc + V _N5 * Ra) / (Ra + Rc) * R2 / (Ra // Rc + R1 + R2)
Here, VN2 is the voltage at the node _N2 , VN5 is the voltage at the node _N5 , and Ra // Rc indicates a parallel combination of resistors Ra and Rc.

Therefore, this circuit supplies a weighted sum. Of course, many other passive circuit designs can be used.

Alternatively, R2 may be an open circuit and R1 may be a short circuit so that there is a simple voltage divider between N2 and N5.

As shown in FIG. 10B, the current signal Sense instead shorts R1 and connects the Sense node to a fixed voltage (eg, IC pin) instead of grounding through R2. Can be generated. In that case, the current entering the pin or the current drawn from the pin represents the output voltage of the driver. Therefore, the coupling circuit may have a circuit for generating a detection signal current.

When the constant voltage of the Issue node is zero (grounded), Ca and Cc can be omitted. If the constant voltage is not equal to zero, at least Cc is needed to support the DC voltage of the pin, but Ca is omitted as long as the voltage at node N2 is greater than the constant voltage. Can be done.

The series capacitors enable, for example, the AC signal processing described above with reference to FIG.

As mentioned above, the present invention is particularly attractive in circuits such as LCC converters where a magnetic element (Lres) that carries the same current as the primary winding of the transformer already exists.

However, not all circuits with isolated outputs already have a magnetic component such as Lres that conducts the same current as the leakage current of the output transformer (or a scaled version of the leakage current). .. In such cases, an additional series inductance (ie, forming LresA) can be added to the existing circuit, providing an additional volume that provides the functionality of the LresB function to create the desired node N5. It may be provided with a wire. In that case, the first inductor LresA is kept small because it is not a required component of the power supply circuit.

Inductors LresA and LresB are referred to as first and second inductors. As described above, they may be separate parts (ie, windings) of a single inductor structure, or they may be separate inductors.

The present invention provides improvements that can be applied to (LED) drivers having output transformers with isolated outputs. The present invention is particularly attractive for use in LCC-type resonant converter stages, such as those often used in isolated LED drivers.

Those skilled in the art will be able to understand and achieve modifications to the disclosed embodiments from studies of the drawings, the specification and the appended claims in the practice of the claimed invention. In the claims, the word "have" does not exclude other elements or steps, and the singular notation does not exclude pluralities. A single processor or other unit may perform the functions of multiple items listed in the claims. Simply, the fact that certain means are listed in different dependent claims does not indicate that the combination of these means cannot be used in an advantageous manner. Any reference code in the claims should not be construed as limiting the scope.

Claims (13)

An inverter having a high-side switch and a low-side switch, wherein the high-side switch and the low-side switch are connected in series with a first node between the high-side switch and the low-side switch.
A transformer with a primary winding and a secondary winding,
A first inductor in series with the primary winding and connected to the primary winding at the second node,
A second inductor that is magnetically coupled to the first inductor, a second inductor that defines an output terminal at one end, and a controller for controlling the inverter, the voltage at the output terminal. A switch mode power converter having a controller having an input for receiving a signal obtained from.
A switch mode power converter in which the second inductor has an inductance that is approximately equal to or greater than the combined primary side series leakage inductance of the transformer. The converter according to claim 1, further comprising a series capacitor in series with the first inductor and a capacitor in parallel with the secondary winding. The converter according to any one of claims 1 to 2, wherein the controller has an input directly connected to the output terminal. The invention according to any one of claims 1 and 2, wherein the controller has a coupling circuit for coupling a signal at the second node and a signal at the output terminal in order to obtain a detection signal supplied to the controller. Converter. The converter according to claim 4, wherein the coupling circuit has a resistance network for coupling a voltage at the second node and a voltage at the output terminal to supply a detection signal voltage. The converter according to claim 4, wherein the coupling circuit includes a circuit for generating a detection signal current. The converter according to any one of claims 1 to 6, wherein the second inductor has a first end portion connected to the second node and has the output terminal at the second end portion. The converter according to any one of claims 1 to 6, wherein the second inductor has a first end portion to be grounded and the output terminal at the second end portion. The converter according to any one of claims 1 to 8, which has a resonance converter including a resonance tank connected to the first node, wherein the resonance tank has the first inductor. The converter according to any one of claims 1 to 9, further comprising a rectifier connected to the secondary winding and a storage capacitor extending over the output of the rectifier. The converter according to claim 10, wherein the rectifier has a 4-diode bridge connected over the secondary winding. The transformer is a series primary secondary winding and secondary secondary winding, defined between the primary secondary winding and the secondary secondary winding. The converter according to claim 10, further comprising a primary secondary winding and a secondary secondary winding comprising a node, wherein the rectifier has a two diode array. The converter according to claim 10, 11 or 12, and a lighting circuit having a lighting load in parallel with the storage capacitor.

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